In fiber reinforced plastic products of many kinds, for example, airplane skin, automobile bodies, container walls, boat hulls, etc., it is frequently desired to hinge a first movable section to a second fixed section of the product. As one specific illustration, in an airplane wing the aileron is hinged to the main section of the wing. The common practice is to secure one or more preconstructed plastic or metal hinges to the adjoining edges of the two sections which are hinged. The two sections individually may be made as one part and then cut into the sections along the edge where the hinge is later secured. The hinge may be a continuous hinge or may be a series of individual hinges secured to the adjoining edges of the sections by fasteners such as rivets or adhesive, depending on the application and the mechanical specifications of the hinged joint.
Integral hinges are known, for example, molded polypropylene hinge structures have been molded as an integral member in the manufacture of an integral member in the manufacture of polypropylene sheet articles, as disclosed in U.S. Pat. No. 3,222,437.
Molded fiber reinforced plastic (FRP) composites are typically made by applying layers of fibrous reinforcing material against the prepared surface of a mold and impregnating the layers of material with a selected liquid resin to form a laminate which after the resin hardens has the shape of the mold. It is advantageous for environmental and other reasons to use a bag molding procedure in which after the layers of resin impregnated fibrous material have been laid-up against the mold surface, a sheet of rubber or synthetic fabric is applied over the layers and sealed at its edges to the mold in such a way as to form an air-tight bag. Air and the gaseous products produced as the resin hardens are withdrawn from the bag which is caused to be pressed against the resin impregnated fibrous layers by atmospheric pressure while the resin hardens which compresses the laminate. The gaseous products may be passed through a filter to extract environmental harmful components before being discharged to the atmosphere, thereby protecting the environment.